Factor the following expression completely put a, b,c, d as the answer : )

1)x^4(8x-1)^2
=x^4(64x^2-16x+1)
=64x^6-16x^5+x^4

2)(8x^3-x^2)^2
=64x^6-16x^5+x^4

3)x^4(8x-1)(8x+1)
=x^4(64x^2-1)
=64x^6-x^4

4)x^4(64x^2-1)
=64x^6-x^4